kp60nick Posted January 30, 2023 Share Posted January 30, 2023 Hi guys I'm building myself a minitruck always been a huge fan and finally picked up my balls and actually doing it bags and everything. Here's my build up I've been diving into the deep dive on the internet on air ride set ups and pros and cons of all the variations. The difference between bag on bar, bag on diff or bag behind diff (there is cantilever but looks way to tricky and want to keep everything low under tray.) Looking at it at first glance the easiest and best way would be bag on diff. Unfortunately due to the fact I have a cast center diff and I have to put my top link arms to the location where the bag would go instead of center like most other minitrucks with triangle 4 links. So bag behind may work with a bracket off back of diff. Down side this requires more air to lift truck which results in hard ride and less lift. Bag on bar really seem like the only option to suit my application. Gets good lift and rides softer. But I've never seen anyone in nz document bag on bar set up (maybe not looking in the right places.) I haven't seen any details on the bar size? or rose joint/ rod end size? The bars are carrying the whole weight of the rear. The guys in the states seem to use lots of rhs box for mounting their bag on bar. Good idea bad idea? I dont know. I'm a little lost. Cheers Nick Quote Link to comment Share on other sites More sharing options...
RXFORD Posted January 30, 2023 Share Posted January 30, 2023 There is plenty of bag on bar setups in trucks here and every bagged Impala has them too. Mtnz facebook page would yeild some results. If you want to keep it simple, 50x50x4shs with bushes each end would be fine. Makes for an easy bag mount platform. Could use 5/8" or bigger heims but check with your cert man first, he may prefer bushes for the the 2 bottom arms. Make sure the bag is centered side to side in the arm, if its offset, it will twist the bushes/joints. If you run an adjustable lower arm it can only be adjustable at axle end, otherwise upper & lower bag plates will be misaligned if adjusted from front. I'd place the bag close to axle rather than half way up the bar. 2:1 or greater can be spongy and its double(+) the work for the bag. Also need to make sure the shocks work in a ratio suited to the bag ratio. I would run a tuneable valving shock to help dial it in. Get as much triangulation as possible. That bottom pic needs more imo. The more triangulation, the less the joints get loaded stopping sideways movement. You will also need design approval for a bag on bar setup compared to a bag over axle. Also, don't do a reverse link like the top/middle pics you posted. Key word to remember is 'trailing arms'. 3 Quote Link to comment Share on other sites More sharing options...
cletus Posted January 30, 2023 Share Posted January 30, 2023 I had a navara a million years ago that was bagged, same diff as you have. I did a parallel 4 bar with a panhard Panhard is not ideal but if you set it up right theres not a huge amount of movement,obviously watts link would be better. 2 Quote Link to comment Share on other sites More sharing options...
kp60nick Posted January 31, 2023 Author Share Posted January 31, 2023 Thanks for that guys. I definitely need to do more planning but you've given me lots of help. Quote Link to comment Share on other sites More sharing options...
kp60nick Posted January 31, 2023 Author Share Posted January 31, 2023 So I have done myself a scale drawing on paper at this stage. In plan view. I Was wondering if this is on the right track? 30° bar angle and keeping all pivot points in same place gives me a nice 750mm center of joint to joint lower arm. If I go greater angle on bar it seems to compress everything up (shorten the bars.) Is this a bad thing? From research I've done so far, the longer the arm less pinion angle change through the motion? Quote Link to comment Share on other sites More sharing options...
RXFORD Posted January 31, 2023 Share Posted January 31, 2023 Well in terms of the layout, yeh something along those lines is the general idea. The geometry side of things is a bit more involved. Its unlikely that you will end up with the link pickup points in same plane front and rear, and with the same vertical separation (parallel bars) once put through a 4-link calc program or mocked up to scale with cardboard from a side on view. Pinion angle change isn't a bad thing as long as the angle change is close to 'equal but opposite' to the UJ at hanger bearing throughout its travel range. The more important thing to pay attention to, is how much 'plunge' the pinion gets. Obviously the axle moves in an arc, so if it gets too much front to back movement its going to flog out hanger bearings or ram the yoke into the back of gbox. A good starting point for a ute to play around with on an online link calculator, would be setting the lower arms parallel(ish) to ground at ride height and move the uppers around til you get an instant centre somewhere around the front bumper. Cycle it, and see what pinion angle/plunge change there is throughout the expected travel range. Report back once you have had a play, it will give you a crash course in the geometry basics. Generic pic for added confusion. Your link will end up something like the 2nd and 3rd diagram once calculated correctly. 1 Quote Link to comment Share on other sites More sharing options...
cletus Posted January 31, 2023 Share Posted January 31, 2023 This guy has some interesting videos on suspension stuff 3 Quote Link to comment Share on other sites More sharing options...
cletus Posted January 31, 2023 Share Posted January 31, 2023 11 hours ago, kp60nick said: So I have done myself a scale drawing on paper at this stage. In plan view. I Was wondering if this is on the right track? 30° bar angle and keeping all pivot points in same place gives me a nice 750mm center of joint to joint lower arm. If I go greater angle on bar it seems to compress everything up (shorten the bars.) Is this a bad thing? From research I've done so far, the longer the arm less pinion angle change through the motion? a couple of thoughts on your drawing it may make life easier to use a triangulated 4 bar rather than a tri upper link. the reason for that is LVVTA does not allow threaded rod ends to be used when there is a bending load on the threads, unless the joint is rated for the load. i have been part of a discussion on this and the solution suggested was quite involved and required a lot of engineering for it to work. there are other ways of doing it but its probably easier to run 2 seperate straight bars you can download the CCM free from lvvta.org.nz have a read of the suspension chapter there is a bit of info in there on link suspension. you will need to run rod ends/spherical bearings/heim joints for your upper bars at least if using a triangulated 4 bar, bushes have too much deflection unless using similar angles to a factory vehicle ie top bars at 90deg to each other- which wouldnt work well for air suspension. your forward crossmember will likely need triangulating back to the chassis as the loading is in the middle, that's why the narrow end is usually at the diff on a factory setup. top bars look like they would hit the bag mounts at full extension unless you mount the bars high now is the time to figure out what youre going to do long term, if its going to have an engine swap or 5 stud swap or anything like that, need to factor things like that in. you dont want to build a suspension that is ok with a stock z24 but then swap in something with more beans later that then has terrible axle tramp or handling problems hope this helps, been there and fucked it up myself haha 2 1 Quote Link to comment Share on other sites More sharing options...
kp60nick Posted February 1, 2023 Author Share Posted February 1, 2023 Man you guys are are wealth of knowledge! Definitely haven't scared me off just yet. I'm looking forward to the journey ahead of me. Thank you for all your input! Quote Link to comment Share on other sites More sharing options...
kpr Posted February 1, 2023 Share Posted February 1, 2023 There is a excel 4 link calculator floating around which is good. Its pretty hard to get a textbook setup. will likely end up with a compromise somewhere. but so is most factory stuff. I would suggest having a few extra holes either side of what the calculator spits out, at least one end of your links, where room is available. From what i can tell the "instant center" is just a dumbed down way of getting you in the ballpark, that comes from all the other numbers being about right. there is lots to it, some of it doesn't matter too much depending what your trying to achieve, other stuff does. 2 Quote Link to comment Share on other sites More sharing options...
Nominal Posted February 1, 2023 Share Posted February 1, 2023 I built the triangulated 4-link in the Mercury mostly based on what would fit, no calculators. It works OK I suppose, but I had to put the bags behind the diff so the ride quality is a pretty crap. Been done for several years now. You could consider swapping to a hilux diff or similar to get a steel casing then run the upper links to the centre if that helps package it better. 1 Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted February 2, 2023 Share Posted February 2, 2023 Would something like this be worth adapting to your rig? Its nissan, and its already got what you need. 1 Quote Link to comment Share on other sites More sharing options...
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